1. Field of Invention
The invention relates to an antenna device and, in particular, to an antenna device with an elliptic reflective surface.
2. Related Art
The rapid development in radio transmission has brought us many products and technologies for multiple-band transmissions. Many new products are equipped with wireless transmission functions to satisfy consumer's needs.
The radio transmission technology usually uses an antenna to transmit or receive electromagnetic (EM) waves for signal transmissions or receptions. However, when the antenna is transmitting or receiving the EM waves and there is another antenna transmitting or receiving the EM waves in its vicinity, then the two antennas will interfere with each other. For example, a wireless access point (AP) has two antennas for signal reception and emission, respectively. When an antenna is transmitting signals, the other antenna for receiving signals may receive the signal transmitted by the wireless AP itself. Therefore, the wireless AP needs some mechanism to avoid such interference. Therefore, it is always a research problem to avoid the interference between antennas and to achieve higher efficiency.
An early solution is to dispose antennas at a long distance apart. However, a longer distance inevitably increases the length of the cable and the cost. An alternative solution is to eliminate EM interference by absorption or shielding. However, this kind of methods requires additional hardware and thus also increases the cost. In addition, another method is to use an analog circuit or a digital processor to process the signals by delaying them in order to achieve the goal of canceling the signals. However, its drawback is its complicated electronic circuit and technique.
It is therefore an important subject of the invention to provide a simpler mechanism at a lower cost to prevent the EM interference between antennas so that they have higher efficiency.